Blueswitch: Enabling Provably Consistent Configuration of Network Switches

Previous research on consistent updates for distributed network configurations has focused on solutions for centralized network-configuration controllers. However, such work does not address the complexity of modern switch datapaths. Modern commodity switches expose opaque configuration mechanisms, with minimal guarantees for datapath consistency and with unclear configuration semantics. Furthermore, would-be solutions for distributed consistent updates must take into account the configuration guarantees provided by each individual switch - plus the compositional problems of distributed control and multi-switch configurations that considerably transcend the single-switch problems. In this paper, we focus on the behavior of individual switches, and demonstrate that even simple rule updates result in inconsistent packet switching in multi-table datapaths. We demonstrate that consistent configuration updates require guarantees of strong switch level atomicity from both hardware and software layers of switches - even in a single switch. In short, the multiple-switch problems cannot be reasonably approached until single-switch consistency can be resolved.